Executive Summary

Our view of the universe has changed dramatically. Hundreds of planets of startling diversity have been discovered orbiting distant suns. Black holes, once viewed as an exotic theoretical possibility, are now known to be present at the center of most galaxies, including our own. Precision measurements of the primordial radiation left by the big bang have enabled astronomers to determine the age, size, and shape of the universe. Other astronomical observations have also revealed that most of the matter in the universe is dark and invisible and that the expansion of the universe is accelerating in an unexpected and unexplained way. Recent discoveries, powerful new ways to observe the universe, and bold new ideas to understand it have created scientific opportunities without precedent.

This report of the Committee for a Decadal Survey of Astronomy and Astrophysics proposes a broad-based, integrated plan for space- and ground-based astronomy and astrophysics for the decade 2012-2021. It also lays the foundations for advances in the decade 2022-2031. It is the sixth in a sequence of National Research Council (NRC) decadal studies in this field and builds on the recommendations of its predecessors. However, unlike previous surveys, it reexamines unrealized priorities of preceding surveys and reconsiders them along with new proposed research activities to achieve a revitalized and timely scientific program. Another new feature of the current survey is a detailed analysis of the technical readiness and the cost risk of activities considered for prioritization. The committee has formulated a coherent program that fits within plausible funding profiles considering several different budget scenarios based on briefings by the sponsoring agencies—the National Aeronautics and Space Administration, the National Science Foundation, and the Department of Energy. As a result,



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Executive Summary Our view of the universe has changed dramatically. Hundreds of planets of startling diversity have been discovered orbiting distant suns. Black holes, once viewed as an exotic theoretical possibility, are now known to be present at the center of most galaxies, including our own. Precision measurements of the primordial radiation left by the big bang have enabled astronomers to determine the age, size, and shape of the universe. Other astronomical observations have also revealed that most of the matter in the universe is dark and invisible and that the expansion of the universe is accelerating in an unexpected and unexplained way. Recent discoveries, powerful new ways to observe the universe, and bold new ideas to understand it have created scientific opportunities without precedent. This report of the Committee for a Decadal Survey of Astronomy and Astrophysics proposes a broad-based, integrated plan for space- and ground-based astronomy and astrophysics for the decade 2012-2021. It also lays the foundations for advances in the decade 2022-2031. It is the sixth in a sequence of National Research Council (NRC) decadal studies in this field and builds on the recommendations of its predecessors. However, unlike previous surveys, it reexamines unrealized priorities of preceding surveys and reconsiders them along with new proposed research activities to achieve a revitalized and timely scientific program. Another new feature of the current survey is a detailed analysis of the technical readiness and the cost risk of activities considered for prioritization. The committee has formulated a coherent program that fits within plausible funding profiles considering several different budget scenarios based on briefings by the sponsoring agencies—the National Aeronautics and Space Adminis- tration, the National Science Foundation, and the Department of Energy. As a result, 

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new worlds, new HorIzons astronoMy astroPHysIcs  In and recommended priorities reflect an executable balance of scientific promise against cost, risk, and readiness. The international context also played an important role in the committee’s deliberations, and many of the large projects involve international collaboration as well as private donors and foundations. The priority science objectives chosen by the survey committee for the decade 2012-2021 are searching for the first stars, galaxies, and black holes; seeking nearby habitable planets; and advancing understanding of the fundamental physics of the universe. These three objectives represent a much larger program of unprecedented opportunities now becoming within our capability to explore. The discoveries made will surely lead to new and sometimes surprising insights that will continue to expand our understanding and sense of possibility, revealing new worlds and presenting new horizons, the study of which will bring us closer to understanding the cosmos and our place within it. This report recommends a program that will set the astronomy and astro- physics community firmly on the path to answering some of the most profound questions about the cosmos. In the plan, new optical and infrared survey telescopes on the ground and in space will employ a variety of novel techniques to investigate the nature of dark energy. These same telescopes will determine the architectures of thousands of planetary systems, observe the explosive demise of stars, and open a new window on the time-variable universe. Spectroscopic and high-spatial- resolution imaging capabilities on new large ground-based telescopes will enable researchers to discern the physical nature of objects discovered at both shorter and longer wavelengths by other facilities in the committee’s recommended program. Innovative moderate-cost programs in space and on the ground will be enhanced so as to enable the community to respond rapidly and flexibly to new scientific discoveries. Construction will begin on a space-based observatory that employs the new window of gravitational radiation to observe the merging of distant black holes and other dense objects and to precisely test theories of gravity in new regimes that we can never hope to study on Earth. The foundations will be laid for studies of the hot universe with a future X-ray telescope that will search for the first massive black holes, and that will follow the cycling of gas within and beyond galaxies. Scientists will conduct new ground-based experiments to study the highest-energy photons emitted by cosmic sources. At the opposite end of the electromagnetic spectrum, radio techniques will become powerful enough to view the epoch when the very first objects began to light up the universe, marking the transition from a protracted dark age to one of self-luminous stars. The microwave background radiation will be scrutinized for the telltale evidence that inflation actually occurred. Perhaps most exciting of all, researchers will identify which nearby stars are orbited by planets on which life could also have developed. Realizing these and an array of other scientific opportunities is contingent on maintaining and strengthening the foundations of the research enterprise that are

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executIve suMMary  essential in the cycle of discovery—including technology development, theory, computation and data management, and laboratory experiments, as well as, and in particular, human resources. At the same time, the greatest strides in understand- ing often come from bold new projects that open the universe to new discoveries, and such projects thus drive much of the strategy of the committee’s proposed program. This program requires a balance of small, medium, and large initiatives on the ground and in space. The large and medium elements within each size category are as follows: • In Space: (Large-scale, in priority order) Wide-Field Infrared Survey Tele- scope (WFIRST)—an observatory designed to settle essential questions in both exoplanet and dark energy research, and which will advance topics ranging from galaxy evolution to the study of objects within our own galaxy. The Explorer Program—augmenting a program that delivers a high level of scientific return on relatively moderate investment and that provides the capability to respond rapidly to new scientific and technical breakthroughs. Laser Interferometer Space Antenna (LISA)—a low-frequency gravitational wave observatory that will open an entirely new window on the cosmos by measuring ripples in space-time caused by many new sources, includ- ing nearby white dwarf stars, and will probe the nature of black holes. International X-ray Observatory (IXO)—a powerful X-ray telescope that will transform our understanding of hot gas associated with stars and galaxies in all evolutionary stages. (Medium-scale, in rank order) New Worlds Technology Development Program—a competed program to lay the technical and scientific foundation for a future mission to study nearby Earth-like planets. Inflation Probe Technology Development Program—a competed program designed to prepare for a potential next-decade cosmic microwave-background mission to study the epoch of inflation. • On the Ground: (Large-scale, in priority order) Large Synoptic Survey Telescope (LSST)—a wide-field optical survey telescope that will transform observation of the variable universe and will address broad questions that range from indicating the nature of dark energy to determining whether there are objects that may collide with Earth. Mid-Scale Innovations Pro- gram augmentation—a competed program that will provide the capability to respond rapidly to scientific discovery and technical advances with new telescopes and instruments. Giant Segmented Mirror Telescope (GSMT)—a large optical and near-infrared telescope that will revolutionize astronomy and provide a spectroscopic complement to the James Webb Space Tele- scope (JWST), the Atacama Large Millimeter/submillimeter Array (ALMA), and LSST. Atmospheric Čerenkov Telescope Array (ACTA)—participation in

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new worlds, new HorIzons astronoMy astroPHysIcs  In and an international telescope to study very high energy gamma rays. (Medium- scale) CCAT (formerly the Cornell-Caltech Atacama Telescope)—a 25-meter wide-field submillimeter telescope that will complement ALMA by under- taking large-scale surveys of dust-enshrouded objects. These major new elements must be combined with ongoing support of the core research program to ensure a balanced program that optimizes overall sci- entific return. To achieve that return the committee balances the program with a portfolio of unranked smaller projects and augmentations to the core research pro- gram, funded by all three agencies. These elements include support of individual investigators, instrumentation, laboratory astrophysics, public access to privately operated telescopes, suborbital space missions, technology development, theoreti- cal investigations, and collaboration on international projects. This report also identifies unique ways that astronomers can contribute to solving the nation’s challenges. In addition, the public will continue to be inspired with images of the cosmos and descriptions of its contents, and students of all ages will be engaged by vivid illustrations of the power of science and technol- ogy. These investments will sustain and improve the broad scientific literacy vital to a technologically advanced nation as well as providing spin-off technological applications to society. The committee notes with appreciation the striking level of effort and involve- ment in this survey contributed by the astronomy and astrophysics community. The vision detailed in this report is a shared vision. RECOMMENDED PROGRAM Maintaining a balanced program is an overriding priority for attaining the overall science objectives that are at the core of the program recommended by the survey committee. More detailed guidance is provided in the report, but optimal implementation is the responsibility of agency managers. The small-scale projects recommended in Table ES.1 are unranked and are listed in alphabetical order. The highest-priority ground-based elements in the medium (Table ES.2) and large (Table ES.3) categories are listed in priority order, and the highest-priority space- based elements in the medium (Table ES.4) and large (Table ES.5) categories are also listed in priority order. All cost appraisals are in FY2010 dollars.

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executIve suMMary  Table eS.1 Space and Ground: Recommended activities—Small Scale (alphabetical Order) Cross- budget,a Reference Recommendation agency Science 2012-2021 in Chapter 7 (augmentation NSF broad; key opportunities in $5M/year additional Page 236 to) advanced advanced instrumentation, Technologies and especially adaptive optics and Instrumentation radio instrumentation (augmentation NSF broad realization of science $8M/year additional Page 236 to) astronomy from observational, empirical, and astrophysics and theoretical investigations, Research Grants including laboratory astrophysics Program (augmentation NaSa broad $35M additional Page 219 to) astrophysics Theory Program (Definition of) a NaSa Technology development $40M Page 219 future ultraviolet- benefiting a future ultraviolet optical space telescope to study hot gas capability between galaxies, the interstellar medium, and exoplanets (augmentation NSF Increased U.S. share of Gemini; $2M/year additional Page 236 to) the Gemini science opportunities include international exoplanets, dark energy, and partnership early-galaxy studies (augmentation NaSa broad; targeted at advancing $2M/year additional, Page 220 to) Intermediate the readiness of technologies at increasing to $15M/ Technology technology readiness levels 3 year additional by Development to 5 2021 (augmentation NaSa basic nuclear, ionic, atomic, and $2M/year additional Page 220 to) laboratory molecular physics to support astrophysics interpretation of data from JWST and future missions (U.S. contribution NaSa Understanding the birth of $150M Page 218 to JaXa-led) SPICa galaxies, stars, and planets; mission cycling of matter through the interstellar medium (augmentation NaSa broad, but including especially $15M/year additional Page 221 to) the Suborbital cosmic microwave background Program and particle astrophysics (augmentation NSF Optical-infrared investments $2.5M/year additional Page 236 to) the Telescope to leverage privately operated System Instrument telescopes and provide Program competitive access to U.S. community Theory and NaSa broad; targeted at high-priority $5M/year NaSa Page 222 Computation NSF science through key projects $2.5M/year NSF Networks DOe $2M/year DOe a Recommended budgets are in FY2010 dollars and are committee-generated and based on available community input.

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new worlds, new HorIzons astronoMy astroPHysIcs  In and Table eS.2 Ground: Recommended activities—Medium Scale appraisal of appraisal Costs Through of annual Constructiona Operations Costsd (U.S. Federal Cross- Technical Share, (U.S. Federal Reference Recommendationb Riskc Science 2012-2021) Share) in Chapter 7 CCaT Submillimeter Medium $140M $11M Page 234 —Science early surveys enabling ($37M) ($7.5M) 2020s broad extragalactic, —University-led, galactic, and 33% federal share outer-solar-system science a The survey’s construction-cost appraisal for CCaT is based on the survey’s cost, risk, and technical readi - ness evaluation (i.e., the cost appraisal and technical evaluation, or CaTe, analysis) and project input, in FY2010 dollars. b The survey’s appraisal of the schedule to first science is based on CaTe analysis and project input. c The risk scale used was low, medium low, medium, medium high, and high. d The survey’s appraisal of operations costs, in FY2010 dollars, is based on project input. Table eS.3 Ground: Recommended activities—large Scale (Priority Order) appraisal of appraisal Costs Through of annual Constructiona Operations Costsd (U.S. Federal Cross- Technical Share, (U.S. Federal Reference Recommendationb Riskc Science 2012-2021) Share) in Chapter 7 1. lSST Dark energy, dark Medium $465M $42M Page 223 —Science late matter, time-variable low ($421M) ($28M) 2010s phenomena, —NSF/DOe supernovae, Kuiper belt and near-earth objects 2. Mid-Scale broad science; peer- N/a $93M to Page 225 Innovations reviewed program $200M Program for projects that fall —Science mid-to- between the NSF late 2010s MRI and MReFC limits 3. GSMT Studies of the Medium $1.1b to $36M to $55M Page 228 —Science mid- earliest galaxies and to $1.4b ($9M to 2020s galactic evolution; medium ($257M to $14M) —Immediate detection and high $350M) partner choice for characterization of ~25% federal share planetary systems continued

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executIve suMMary  Table eS.3 Continued appraisal of appraisal Costs Through of annual Constructiona Operations Costsd (U.S. Federal Cross- Technical Share, (U.S. Federal Reference Recommendationb Riskc Science 2012-2021) Share) in Chapter 7 4. aCTa Indirect detection Medium $400M Unknown Page 232 —Science early of dark matter; low ($100M) 2020s particle acceleration —NSF/DOe; U.S. and active galactic join european nucleus science ˇ Cerenkov Telescope array a The survey’s construction-cost appraisals for the large Synoptic Survey Telescope (lSST), Giant Segmented ˇ Mirror Telescope (GSMT), and atmospheric Cerenkov Telescope array (aCTa) are based on the survey’s cost, risk, and technical readiness evaluation (i.e., the cost appraisal and technical evaluation, or CaTe, analysis) and project input, in FY2010 dollars; cost appraisals for the Mid-Scale Innovations Program augmentation are committee- generated and based on available community input. For GSMT the cost appraisals are $1.1 billion for the Giant Magellan Telescope (GMT) and $1.4 billion for the Thirty Meter Telescope (TMT). Construction costs for GSMT could continue into the next decade, at levels of up to $95 million for the federal share. The share for the U.S. government is shown in parentheses when it is different from the total. b The survey’s appraisals of the schedule to first science are based on CaTe analysis and project input. c The risk scale used was low, medium low, medium, medium high, and high. d The contractor had no independent basis for evaluating the operations cost estimates provided for any ground- based project. The survey’s appraisals for operations costs, in FY2010 dollars, were constructed by the survey committee on the basis of project input and the experience and expertise of its members. For GSMT the range in operations costs is based on estimates from GMT ($36 million) and TMT ($55 million). The share for the U.S. government is shown in parentheses when it is different from the total. Table eS.4 Space: Recommended activities—Medium-Scale (Priority Order) Cross- Reference appraisal of Costsa Recommendation Science in Chapter 7 1. New Worlds Preparation for a planet-imaging mission $100M to $200M Page 215 Technology beyond 2020, including precursor Development Program science activities 2. Inflation Probe Cosmic microwave background (CMb)/ $60M to $200M Page 217 Technology inflation technology development and Development Program preparation for a possible mission beyond 2020 aThe survey’s cost appraisals are in FY2010 dollars and are committee-generated and based on available com - munity input.

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new worlds, new HorIzons astronoMy astroPHysIcs  In and Table eS.5 Space: Recommended activities—large-Scale (Priority Order) appraisal of Costsa Total Cross- launch Technical (U.S. U.S. Share, Reference Dateb Riskc Recommendation Science Share) 2012-2021 in Chapter 7 1. WFIRST 2020 Dark energy, Medium $1.6b $1.6b Page 205 —NaSa/DOe exoplanets, and low collaboration infrared survey- science 2. augmentation Ongoing enable rapid low $463M $463M Page 208 to explorer response to science Program opportunities; augments current plan by 2 Medium- scale explorer (MIDeX) missions, 2 Small explorer (SMeX) missions, and 4 Missions of Opportunity (MoOs) Mediume 3. lISa 2025 Open low-frequency $2.4b $852M Page 209 —Requires eSa gravitational- ($1.5b) partnershipd wave window for detection of black- hole mergers and compact binaries and precision tests of general relativity 4. IXO 2020s black-hole accretion Medium $5.0b $200M Page 213 —Partnership and neutron- high ($3.1b) with eSa and star physics, JaXad matter/energy life cycles, and stellar astrophysics a The survey’s cost appraisals for Wide-Field Infrared Survey Telescope (WFIRST), laser Interferometer Space antenna (lISa), and International X-ray Observatory (IXO) are based on the survey’s cost, risk, and technical readi- ness evaluation (i.e., the cost appraisal and technical evaluation, or CaTe, analysis) and project input, in FY2010 dollars for phase a costs onward; cost appraisals for the explorer augmentation and the medium elements of the space program are committee-generated, based on available community input. The share for the U.S. government is shown in parentheses when it is different from the total. The U.S. share is based on the United States assuming a 50 percent share of costs and includes an allowance for extra costs incurred as a result of partnering. b The survey’s appraisal of the schedule to launch is the earliest possible based on CaTe analysis and project input. c The risk scale used was low, medium low, medium, medium high, and high. d Note that the lISa and IXO recommendations are linked—both are dependent on mission decisions by the european Space agency (eSa) and the Japan aerospace exploration agency (JaXa). e Technical risk assessment of “medium” is contingent on a successful lISa Pathfinder mission.